Mosasaur - A genus (the type of the family Mosasauridae) of large, extinct, aquatic, fish-eating lizards related to the recent monitors but having limbs modified into swimming paddles.

an extinct aquatic lizard that reached twenty to thirty feet in length and fed on fish and ammonites.

Mosasaurs were giant, carnivorous marine reptiles (but not dinosaurs) that lived during the late Cretaceous period. They were powerful swimmers that had four paddle-like limbs on a long, streamlined body. The large head had large jaws with many teeth. They hunted fish, turtles, mollusks, and shellfish. Some Mosasaurs include the Mosasaurus (33 feet=10 m long with sharp teeth from the North Atlantic), Platecarpus, Tylosaurus (26 feet=8 m long with sharp teeth from the North and South Atlantic), Plotosaurus, Clidastes, Plioplatecarpus, and Globidens (with flat teeth for crushing shellfish). The first Mosasaur, Mosasaurus hoffmani, was found in the Netherlands in 1780.

Mosasaurs (from Latin Mosa meaning the 'Meuse river' in the Netherlands, and Greek sauros meaning 'lizard') were serpentine marine reptiles. The first fossil remains were discovered at the Meuse river about 1780. These ferocious marine predators are considered by some experts to be closely related to snakes, due to extreme similarities in jaw and skull anatomies.Lee, 1997, "The phylogeny of varanoid lizards and the affinities of snakes," in Phil.